[Paper Review] Astrophysical Tests of Dark Matter Self-Interactions

Susmita Adhikari, Arka Banerjee+12 more|arXiv (Cornell University)|Jul 21, 2022

Dark Matter and Cosmic PhenomenaPhysics and Astronomy46 citations

TL;DR

A comprehensive review of self-interacting dark matter (SIDM): theory, macroscopic effects on halos from dwarfs to clusters, observational constraints, degeneracies with baryons, and future tests.

ABSTRACT

Self-interacting dark matter (SIDM) arises generically in scenarios for physics beyond the Standard Model that have dark sectors with light mediators or strong dynamics. The self-interactions allow energy and momentum transport through halos, altering their structure and dynamics relative to those produced by collisionless dark matter. SIDM models provide a promising way to explain the diversity of galactic rotation curves, and they form a predictive and versatile framework for interpreting astrophysical phenomena related to dark matter. This review provides a comprehensive explanation of the physical effects of dark matter self-interactions in objects ranging from galactic satellites (dark and luminous) to clusters of galaxies and the large-scale structure. The second major part describes the methods used to constrain SIDM models including current constraints, with the aim of advancing tests with upcoming galaxy surveys. This part also provides a detailed review of the unresolved small-scale structure formation issues and concrete ways to test simple SIDM models. The review is rounded off by a discussion of the theoretical motivation for self-interactions, degeneracies with baryonic and gravitational effects, extensions to the single-component elastic-interactions SIDM framework, and future observational and theoretical prospects.

Motivation & Objective

• Explain the motivation for SIDM as a solution to cusp/core and missing satellites problems and its broader impact on halo structure.
• Synthesize how microscopic DM scattering translates into macroscopic phenomenology across galaxies, clusters, and large-scale structure.
• Survey observational and simulation-based constraints on the SIDM cross section and its velocity dependence.
• Discuss extensions beyond simple elastic SIDM and outline future experimental and observational prospects.

Proposed method

• Define cross sections (sigma, sigma/m_DM) and their velocity/angle dependences, including sigma_T and sigma_V variants.
• Describe how to map microscopic interactions to macroscopic transport properties via collision rates and energy/momentum transfer considerations.
• Explain Monte Carlo SIDM implementations in N-body simulations and how scattering probabilities are computed between particle pairs.
• Summarize analytical and numerical tests used to validate SIDM implementations (wind tunnel, Hernquist-profile tests, etc.).
• Discuss how velocity-dependent and angular-dependent scattering alter expectations across different halo mass scales.

Experimental results

Research questions

• RQ1 What are the effective macroscopic signatures of DM self-interactions in halos from galactic to cluster scales?
• RQ2 How do velocity and angular dependences in SIDM affect observational constraints across systems with different characteristic velocities?
• RQ3 What are the main degeneracies between SIDM effects and baryonic or gravitational physics that can mimic or hide self-interactions?
• RQ4 What are the prospects and methods for constraining SIDM with upcoming galaxy surveys and simulations?

Key findings

• SIDM readily produces core-like inner density profiles and can lead to gravothermal phenomena in halos.
• Self-interactions modify subhalo survival and tidal stripping, influencing satellite populations and halo shapes.
• Velocity dependence and scattering angular distribution are crucial; they can suppress cross sections in clusters while remaining impactful in galaxies.
• Cross-section per unit mass of order ~1 cm^2/g is often required for noticeable halo-scale effects given typical halo column densities.
• Degeneracies with baryonic processes and alternative gravity/dark sector physics complicate interpretation of SIDM signals.
• Observational constraints span strong lensing, stellar streams, X-ray and weak lensing in clusters, dwarf galaxies, and large-scale structure; future surveys promise tighter limits.